Pitchfork Analysis of Class II Correction using Forsus FRD

Transcription

1 /jp-journals ORIGINAL ARTICLE Meenu Goel et al Pitchfork Analysis of Class II Correction using Forsus FRD 1 Meenu Goel, 2 Saurabh Sonar, 3 Mudita Srivastav, 4 Puneet Batra, 5 Anurag Bhagat ABSTRACT Introduction: A paradigm shift in nonsurgical treatment modality, i.e. fixed functional appliances have been shown to correct the overjet and the Class II molar relationship via a combination of skeletal and dental changes. Aim: To evaluate the skeletal and dental changes using Forsus Fatigue Resistant Device (FRD) (3M Unitek Corp, Monrovia, California, USA) in young adults during Class II correction. Materials and methods: Lateral cephalograms of post leveling and aligning sample (T1) and post Forsus sample (T2) of 10 orthodontically treated young adult patients (CVMI-CS5) with borderline skeletal Class II malocclusion (ANB = 3-7 ) due to mandibular retrognathism, requiring skeletal mandibular sagittal correction were selected. The skeletal and dental treatment changes were analyzed using the Pitchfork analysis (PFA). Results: The PFA showed that the maxilla and mandible moved mesially by 0.3 and 3.2 mm, respectively; the average apical base change was 2.9 mm. The maxillary molar moved distally 0.5 mm, and the mandibular molar moved mesially 1.6 mm. Molar intercuspation changed by 5 mm. The upper incisor moved palatally by 1.5 mm, and the lower incisor moved labially by 2.8 mm. Total overjet change was 6.2 mm. Conclusion: The FRD protocol led to a successful correction of Class II malocclusion with more of skeletal than dental correction. However, more parameters are required to assess the mandibular growth and remodeling of the glenoid fossa. Keywords: Pitchfork analysis, Forsus FRD, Class II malocclusion. How to cite this article: Goel M, Sonar S, Srivastav M, Batra P, Bhagat A. Pitchfork Analysis of Class II Correction using Forsus FRD. J Ind Orthod Soc 2013;47(4): INTRODUCTION Class II malocclusion presents a major and common challenge to orthodontists. Numerous orthodontic techniques and appliances have been introduced to treat Class II malocclusions, including intra-arch and interarch appliances, extraoral appliances, selective extraction patterns, and surgical repositioning of the jaws. Class II skeletal malocclusions are commonly treated with fixed appliance therapy or with a functional appliance followed by a fixed appliance. Recent studies suggested that fixed functional appliances can be effective in correcting Class II skeletal abnormalities by promoting growth of the mandible and remodeling of the glenoid fossa. 1-3 It has been reported that the effectiveness of functional therapy depends on both the treatment timing (skeletal maturity 1,3 Senior Lecturer, 2 Professor, 4 Professor and Head, 5 Reader 1-5 Department of Orthodontics, Institute of Dental Studies and Technologies, Ghaziabad, Uttar Pradesh, India Corresponding Author: Meenu Goel, Senior Lecturer, Department of Orthodontics, Institute of Dental Studies and Technologies, Delhi- Meerut Road, Kadrabad, Modinagar, Ghaziabad, Uttar Pradesh, India Phone: , dr_meenugoel@yahoo.co.in Received on: 24/8/12 Accepted after Revision: 14/2/13 at the start of functional therapy) and the type of functional appliance. 4-6 According to several studies, mandibular growth can extend beyond puberty, and minimal residual growth can only be stimulated with fixed functional appliances Ruf and Pancherz, 8-9 Konik et al, 10 and Kinzinger and Diedrich 11 stated that the treatment of late adolescents and young adults with rigid fixed functional appliances, such as the Herbst or functional mandibular advancement resulted in correction of the Class II malocclusion with the skeletal and dental changes. The present study was designed to evaluate the skeletal and dental changes using Forsus Fatigue Resistant Device (FRD) (3M Unitek Corp, Monrovia, California, USA) in young adults during Class II correction. MATERIALS AND METHODS A post leveling and aligning sample (T1) of orthodontically treated patients was selected from the Department of Orthodontics of Institute of Dental Studies and Technologies (IDST), Kadrabad, Modinagar, India. The criteria for patient selection were: Young adult patients (CVMI-5) 12 with borderline skeletal Class II malocclusion (ANB = 3 to 7 ) due to mandibular retrognathism, requiring skeletal mandibular sagittal correction. As the correlation values between Fishman maturation prediction (FMP) method and cervical vertebral maturation (CVM) method are moderately high. 13 A distinctive advantage of the cervical maturity evaluation 240

2 JIOS Pitchfork Analysis of Class II Correction using Forsus FRD is that it does not imply extraradiation exposure for the patient. Presence of permanent dentition up to 2nd molars. Pretreatment permanent dentition with a minimum of half the cusp width of Class II molar relation. Increased overjet, not less than 5 mm. Positive pretreatment visual treatment objective (VTO). Treatment completed without any permanent teeth extracted (excluding third molars). Good quality pretreatment and post-treatment cephalometric radiographs. A total of 10 subjects were included in this trial after consultation with the statistician. The patients underwent functional appliance phase over a period of minimum 6 months. Patients were treated with MBT preadjusted edgewise appliance. Before insertion of Forsus FRD the maxillary and mandibular dental arches were stabilized with the help of " " stainless steel wire, torque of 10 was introduced in the lower anterior segment and the wires were cinched back distal to molars. A Guerin lock was also placed distal to the canine bracket. Forsus FRD spring was placed in maxillary first molar head gear tube and distal to the mandibular Figs 1A to C: (A) Pretreatment after leveling and aligning, (B) forsus FRD spring for mandibular advancement, (C) post-treatment after mandibular advancement Fig. 2A: Pitchfork superimposition 1. The superimposition is on the nasal line, palatal curvature and anterior contour of key ridge. All measurements are carried out parallel to the mean functional occlusal plane (MFOP). Maxilla is measured at the SE-points, ABCH at the D-points, and upper molar change at the mesial contact points and incisor-change at the incisal edges Fig. 2B: Pitchfork superimposition 2. The tracings are displaced along the MFOP until the D-points are lying on a common perpendicular line to MFOP. Again all the measurements are undertaken parallel to MFOP. Lower molar change is measured at the mesial contact points and incisor change at the incisal edges Fig. 2C: Pitchfork superimposition 3. The tracings are displaced again until the mesial contact points of the upper molars are lying on a common perpendicular line to MFOP. The molar intercuspation change is measured at the mesial contact points of the lower molars Fig. 2D: Pitchfork superimposition 4. The tracings are displaced again until the incisal edges of the upper incisors are lying on a common perpendicular line to MFOP. The overjet change is measured at the incisal edges of the lower incisors The Journal of Indian Orthodontic Society, October-December 2013;47(4):

3 Meenu Goel et al both groups. The upper and lower incisors were moved mesially. Overjet was improved in all patients. The study showed a decrease of saddle angle by 1.0 ± 0.6. DISCUSSION Fig. 3: Diagram of pitchfork analysis (maxilla+ mandible = ABCH; ABCH + U6 + L6 = 6/6; ABCH + U1+ L1 = 1/1) canine. The stepwise advancement of the mandible was done with initial advancement of 4 to 5 mm, followed by incremental advancement of 2 mm after 2 months, if required. This was maintained for a period of minimum of 6 months (Figs 1A to C). The pretreatment and post-treatment cephalometric radiographs were hand-traced on acetate paper. In order to describe the sagittal treatment changes that occurred, the radiographs were analyzed using the pitchfork analysis (PFA). 14 The PFA accounts for and summarizes sagittal mandibular and maxillary molar movements, sagittal maxillary and mandibular advancement relative to the cranial base, and the combination of all of these movements in correcting the molar relationship. Distal maxillary skeletal and dental movements and mesial mandibular skeletal and dental movements, which aid in Class II correction, were assigned positive values. Movements that worsen Class II relations were assigned negative values. Incisor movements that affect overjet were also measured and summarized. All measurements were made at the level of the functional occlusal plane, which was drawn through the occlusal contact points of the molars and premolars. RESULTS The tracings were superimposed as described by Johnston 14 (Figs 2A to D). All measurements are described positive if they contribute to Class II correction and negative if they aggravate Class II relationship. The PFA showed that the maxilla and mandible moved mesially by 0.3 and 3.2 mm, respectively; the average apical base change was 2.9 mm. The maxillary molar moved distally 0.5 mm, and the mandibular molar moved mesially 1.6 mm. Molar intercuspation changed by 5 mm. The upper incisor moved palatally by 1.5 mm, and the lower incisor moved labially by 2.8 mm. Total overjet change was 6.2 mm (Table 1 and Fig. 3). During treatment, the mandible and maxilla moved mesially, with the mandible moving more than the maxilla in The goal of functional appliance therapy is to encourage or to redirect the growth in a favorable direction. Several functional appliances are presented in the literature for the correction of Class II division 1 malocclusion. The major differences in the effects between various orthopedic appliances are mainly related to the technique of fabrication, construction bites, and hours of wear. Removable appliances are considered uncomfortable and unesthetic by many patients and require patient compliance. Consequently, a primary advantage of fixed functional appliances is independence from the need for patient cooperation. The present study has evaluated the dental and skeletal effects using PFA in young adults treated with Forsus FRD. The PFA enables a clear distinction between skeletal and dental changes in the sagittal dimension to describe therapeutic effects caused by treatment strategies on orthodontic Class II patients. Measurement data are usually recorded in the form of diagrams that give the appearance of pitchforks. The diagrams provide differential insight and permit informative comparisons. 14 The results showed that the molar relationships of patients treated were corrected primarily due to mandibular growth changes. Anterior mandibular displacement accounted for 3.2 mm or approximately 64% of the 5 mm molar correction. Mesial mandibular molar movements accounted for 32% of the total correction. In contrast, treatment changes in the maxilla worked against the molar corrections, with anterior maxillary skeletal movement of 6% and distal dental movements of 10%. Many previous studies also reported restriction in the forward growth of maxilla by twin-block, by other mandibular protraction appliances, 20 and also by many other functional appliances. 15,17,21 However, few studies reported no restraint effect in the forward movement of maxilla by the removable 22,23 and fixed functional appliances. 24,25 Thus, the design of the appliance was not a major factor in the headgear effect of functional appliance therapy. Table 1: Comparison of pretreatment and post-treatment variables and treatment changes in the and Forsus FRD groups Variable Mean SD Maxilla (mm) Mandibular (mm) ABCH (mm) U L U6/L U L U1/L

4 JIOS Pitchfork Analysis of Class II Correction using Forsus FRD A net reduction of 6.2 mm was recorded for the overjet, while a net improvement of 5 mm was obtained for the molar relationship which accounts for the Class II correction. Lower incisor moved labially by 2.8 mm which contributed to 45.2% of overjet correction. Upper incisor moved palatally by 1.5 mm thus contributed to 8% of overjet reduction. A general overview of the effects of Class II treatment with Forsus FRD leads to the consideration that skeletally one of the main outcomes of this protocol consists of a significant change in the sagittal position of the mandible. This mandibular advancement can be because of remodeling of the glenoid fossa or mandibular growth. The saddle angle was evaluated to assess the skeletal changes which showed a decrease of 1.0 ± 0.6. According to Rabie et al 26 the Indian hedgehog gene is the mechanotransduction mediator in the condyle. The expression of Indian hedgehog elicited by mechanical loading of the mandibular joint promoted mesenchymal cell proliferation and initiated a cascade of cellular and molecular responses that led to condylar growth. Indian hedgehog, a member of the vertebrate hedgehog morphogen family, was reported to be key morphogen during skeletal development and regeneration. On the other hand, the skeletal outcomes of the FRD protocol with regard to the maxilla appeared to be rather limited. The lack of a significant effect of the FRD on the sagittal position of the maxilla might be correlated with the short duration of active treatment and the normal growth of maxilla. Retroclination of the maxillary incisors (U1) and proclination of mandibular incisors (L1) are a widely accepted consensus with various functional appliances. 27 In present study, the upper incisors tipped palatally by 1.5 mm. The palatal movement of the U1 was due to the reciprocal force that acted distally on the maxillary dental arch. The mandibular incisors tipped labially by 2.8 mm in present study. This could be due to the mesial force on the L1 induced by the forward posture of the mandible. This finding is in accordance with the effects of other functional appliances. 25 Various researches showing skeletal and dental changes with different functional appliances are tabulated in Table 2. The outcomes reported in the current study refer to the end of comprehensive Class II treatment. However, it should be noted that more than half of the patients in the FRD group completed their treatment protocols at very advanced post pubertal stages in skeletal maturation (CS5 or CS6). The amount of craniofacial growth occurring after those stages is very limited in Class II subjects, and, more importantly, growth differences between Class II and normal occlusion subjects Table 2: Studies of different functional appliances Functional appliance Amount of Amount of skeletal change dental change Modified twin block 28 70% 30% Herbst appliance % 40% Jasper Jumper 33 40% 60% Eureka Spring 34 10% 90% after late puberty are insignificant. When orthodontic therapy of Class II malocclusion is completed at late puberty, close to completion of active craniofacial growth, relapse tendency due to a re-establishment of Class II growth characteristics is expected to occur less often. As there are many factors involved in the correction of disproportionate jaw relationships, therefore above-mentioned findings should be interpreted with caution. Further studies including more parameters and larger sample size are required and the results of a long term follow-up are essential to address issues of stability. CONCLUSION The FRD protocol led to a successful correction of Class II malocclusion. The protocol had a greater skeletal effect on the mandibular structures by advancing the mandible and mesial movement of mandibular molars. The appliance was not efficient in restricting the forward growth of the maxilla. At the dentoalveolar level, a large amount of mesial movement of the lower incisors and first molars occurred. REFERENCES 1. McNamara JA Jr, Carlson DS. Quantitative analysis of temporomandibular joint adaptation to protrusive function. Am J Orthod 1979 Dec;76(6): Woodside DG, Metaxas A, Altuna G. The influence of functional appliance therapy on glenoid fossa remodelling. Am J Orthod Dentofacial Orthop 1987 Sep;92(3): Paulsen HU, Karle A, Bakke M, Heskind A. 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